Breakaway support post for highway guardrail end treatments

ABSTRACT

A support post for a guardrail has a strong axis and a weak axis which is substantially perpendicular to the strong axis. The support post is adapted to receive a guardrail such that the rail face of the guardrail runs generally perpendicular to the strong axis such that the support post resists an impact on the face of the guardrail and yields to an impact force on the end of the guardrail.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser.No. 60/046,015 filed May 9, 1997.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to highway guardrail systems having aguardrail mounted on posts, and more particularly, to guardrail endtreatments designed to meet applicable federal and state safetystandards including but not limited to crash worthiness requirements.

BACKGROUND OF THE INVENTION

Along most highways there are hazards which present substantial dangerto drivers and passengers of vehicles if the vehicles leave the highway.To prevent accidents from a vehicle leaving a highway, guardrail systemsare often provided along the side of the highway. Experience has shownthat guardrails should be installed such that the end of a guardrailfacing oncoming traffic does not present another hazard more dangerousthan the original hazard requiring installation of the associatedguardrail systems. Early guardrail systems often had no protection atthe end facing oncoming traffic. Sometimes impacting vehicles becameimpaled on the end of the guardrail causing extensive damage to thevehicle and severe injury to the driver and/or passengers. In somereported cases, the guardrail penetrated directly into the passenger'scompartment of the vehicle fatally injuring the driver and passengers.

Various highway guardrail systems and guardrail end treatments have beendeveloped to minimize the consequences resulting from a head-on impactbetween a vehicle and the extreme end of the associated guardrail. Oneexample of such end treatments includes tapering the ends of theassociated guardrail into the ground to eliminate potential impact withthe extreme end of the guardrail. Other types of end treatments includebreakaway cable terminals (BCT), vehicle attenuating terminals (VAT),the SENTRE end treatment, and breakaway end terminals (BET).

It is desirable for an end terminal assembly installed at one end of aguardrail facing oncoming traffic to attenuate any head-on impact withthe end of the guardrail and to provide an effective anchor to redirecta vehicle back onto the associated roadway after a rail face impact withthe guardrail downstream from the end terminal assembly. Examples ofsuch end treatments are shown in U.S. Pat. No. 4,928,928 entitledGuardrail Extruder Terminal, and U.S. Pat. No. 5,078,366 entitledGuardrail Extruder Terminal.

A SENTRE end treatment often includes a series of breakaway steelguardrail support posts and frangible plastic containers filled withsandbags. An impacting vehicle is decelerated as the guardrail supportposts release or shear and the plastic containers and sandbags arecompacted. A cable is often included to guide an impacting vehicle awayfrom the associated guardrail.

A head-on collision with a guardrail support post located at the end ofa guardrail system may result in vaulting the impacting vehicle.Therefore, guardrail end treatments often include one or more breakawaysupport posts which will yield or shear upon impact by a vehicle.Examples of previously available breakaway posts are shown in U.S. Pat.No. 4,784,515 entitled Collapsible Highway Barrier and U.S. Pat. No.4,607,824 entitled Guardrail End Terminal. Posts such as shown in the'515 and the '824 Patents include a slip base with a top plate and abottom plate which are designed to not yield upon lateral impact. Whensufficient axial impact force is applied to the upper portion of theassociated post, the top plate and the bottom plate will slide relativeto each other. If a vehicle contacts the upper part of the post, theassociated impact forces tend to produce a bending moment which mayreduce or eliminate any slipping of the top plate relative to the bottomplate. Also, improper installation of the top plate relative to thebottom plate, such as over tightening of the associated mechanicalfasteners, may prevent proper functioning of the slip base. A breakawaysupport post is also shown in U.S. Pat. No. 5,503,495 entitledThrie-Beam Terminal with Breakaway Post Cable Release.

Wooden breakaway support posts are frequently used to releasably anchorguardrail end treatments and portions of the associated guardrail. Suchwooden breakaway support posts, when properly installed, generallyperform satisfactorily to minimize damage to an impacting vehicle duringeither a rail face impact or a head-on impact. However, impact of avehicle with a wooden breakaway support post may often result insubstantial damage to the adjacent soil. Removing portions of a brokenwooden post from the soil is often both time consuming and furtherdamages the soil. Therefore, wooden breakaway support posts are ofteninstalled in hollow metal tubes, sometimes referred to as foundationsleeves, and/or concrete foundations. For some applications, one or moresoil plates may be attached to each metal sleeve to further improve thebreakaway characteristics of the associated wooden post. Such metalsleeves and/or concrete foundations are relatively expensive and timeconsuming to install.

Light poles, sign posts or similar items are often installed next to aroadway with a breakable or releasable connection. For someapplications, a cement foundation may be provided adjacent to theroadway with three or more bolts projecting from the foundation aroundthe circumference of the pole. Various types of frangible or breakableconnections may be formed between the bolts and portions of the lightpole or sign post.

SUMMARY OF THE INVENTION

In accordance with teachings of the present invention, variousshortcomings of previous guardrail support posts associated with highwayguardrail end treatments have been addressed. The present inventionprovides a breakaway support post which will buckle or yield duringhead-on impact by a vehicle at or near the extreme end of an associatedguardrail to minimize damage to the vehicle and provide sufficientstrength to direct a vehicle back onto an associated roadway during arail face impact with the guardrail downstream from the guardrail endtreatment. The use of breakaway support posts incorporating teachings ofthe present invention substantially reduces the time and cost associatedwith initial installation of a guardrail end treatment and repair of theguardrail end treatment following impact by a motor vehicle.

One aspect of the present invention includes providing a breakawaysupport post having one or more slots formed in the support post toallow the support post to buckle or yield in response to forces appliedto the support post in a first direction by an impacting vehicle withoutcausing excessive damage to the vehicle. The orientation and location ofthe slots are selected to allow the support post to effectively anchorthe guardrail to direct an impacting vehicle back onto an adjacentroadway in response to forces applied to the support post in a seconddirection during a downstream rail face impact. For some applications,one or more plates may be attached to the breakaway support post andinserted into the soil to provide additional support during a rail faceimpact with the associated guardrail and to provide more reliablebuckling or yielding of the breakaway support post during a head-onimpact with one end of the associated guardrail. Alternatively, thelength of the portion of the breakaway support post inserted into thesoil may be increased to enhance these same characteristics. For someapplications, the breakaway support post may have a typical I-beam crosssection with slots formed in one or more flange portions of the I-beam.Alternatively, the breakaway support post may have a hollow, rectangularor square cross section with slots formed in one or more sides of thepost in accordance with teachings of the present invention.

Another aspect of the present invention includes providing a breakawaysupport post having a first portion or an upper section and a secondportion or a lower section with the first portion rotatably coupled withthe second portion. A pivot pin or other suitable type of rotatablecoupling preferably connects adjacent ends of the first portion and thesecond portion to allow rotation of the first portion relative to thesecond portion. The pivot pin is preferably oriented during installationof the associate breakaway support post to allow rotation of the firstportion when force is applied thereto in one direction and to blockrotation of the first portion when force is applied thereto in a seconddirection. A shear pin or other suitable releasing mechanism may beprovided to releasably couple the first portion and the second portionaligned longitudinally with each other. The shear pin and pivot pin arepreferably oriented such that during a head-on impact with the end ofthe associated guardrail facing oncoming traffic, the shear pin willfail and allow the upper section to rotate relative to the lower sectionand thus minimize damage to the impacting vehicle. For someapplications, a release bar or push bar may be attached to the lowersection to assist with disengagement of the upper section from the lowersection during such rotation of the upper section. During a rail faceimpact with the associated guardrail, the same orientation of the shearpin and the pivot pin prevents the upper section from rotating relativeto the lower section. Thus, the breakaway support post will buckle oryield during a head-on impact to minimize damage to an impacting vehicleand will remain intact to redirect an impacting vehicle back onto theassociated roadway after a rail face impact.

Technical advantages of the present invention include providingbreakaway support posts which are easier to initially install and torepair as compared to wooden breakaway support posts. Major portions ofeach breakaway support post may be fabricated from standard,commercially available steel I-beams using conventional metal bendingand stamping techniques in accordance with teachings of the presentinvention. One or more metal soil plates may be attached to eachbreakaway support post to further enhance desired characteristics ofyielding or buckling during head-on impact with one end of an associatedguardrail to minimize damage to an impacting vehicle and to securelyanchor the associated guardrail to redirect an impacting vehicle backonto the adjacent roadway after a rail face impact. Breakaway supportposts incorporating teachings of the present invention may be used witha wide variety of guardrail end treatments having various types ofenergy absorbing assemblies located at or near the end of the associatedguardrail facing oncoming traffic. For many applications, breakawaysupport posts may be satisfactorily installed adjacent to the edge of aroadway without the use of steel foundation tubes and/or concretefoundations typically associated with installing wooden breakawaysupport posts and other types of breakaway support posts.

A further aspect of the present invention includes providing guardrailsupport posts having a first portion or upper section attached orcoupled, at least in part, by a frangible connection, to a secondportion or lower section. The support post and frangible connection maybe oriented in accordance with teachings of the present invention toresist impact by a motor vehicle from one direction (strong direction),and to yield to impact by a motor vehicle from another direction (weakdirection). Preferably, the frangible connection allows the upperportion of the post to deflect slightly and then break off of the lowerportion, thus minimizing lifting of the impacting vehicle into the air.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following writtendescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a schematic drawing showing an isometric view with portionsbroken away of a highway guardrail system having a breakaway supportpost with a guardrail mounted thereon in accordance with one embodimentof the present invention;

FIG. 2 is a schematic drawing in elevation with portions broken awayshowing a side view of the highway guardrail system of FIG. 1;

FIG. 3 is a schematic drawing in section of the breakaway support posttaken along lines 3-3 of FIG. 2;

FIG. 4 is a schematic drawing showing an isometric view with portionsbroken away of a highway guardrail system having a breakaway supportpost with a guardrail mounted thereon in accordance with anotherembodiment of the present invention;

FIG. 5 is a schematic drawing in elevation with portions broken awayshowing a side view of the breakaway support post of FIG. 4 in its firstposition;

FIG. 6 is a schematic drawing in elevation with portions broken awayshowing a side view of the breakaway support post of FIG. 5 rotatingfrom its first position to a second position in response to a forceapplied to the breakaway support post in one direction correspondingwith an impact by a vehicle with one end of the associated guardrail;

FIG. 7 is a schematic drawing showing an isometric view with portionsbroken away of a highway guardrail system having a breakaway supportpost with a guardrail mounted thereon in accordance with a furtherembodiment of the present invention;

FIG. 8 is a schematic drawing in elevation with portions broken awayshowing a side view of the highway guardrail system of FIG. 7;

FIG. 9 is a schematic drawing in section of the breakaway support posttaken along lines 9-9 of FIG. 8;

FIG. 10 is a schematic drawing showing an isometric view with portionsbroken away of a highway guardrail system having a breakaway supportpost with a guardrail mounted thereon in accordance with anotherembodiment of the present invention;

FIG. 11 is a schematic drawing in elevation with portions broken awayshowing a side view of a breakaway support post analogous to thebreakaway support post of FIG. 10 rotating from its first position to asecond position and separating in response to a force applied to thebreakaway support post in one direction corresponding with an impact bya vehicle with one end of the associated guardrail;

FIG. 12 is a schematic drawing showing an exploded, isometric view withportions broken away of an alternative embodiment of breaker barssuitable for use with the guardrail system illustrated in FIGS. 10 and11;

FIG. 13 is a schematic drawing in elevation with portions broken awayshowing a side view of the breakaway support post of FIG. 10 utilizingthe breaker bars of FIG. 12 and rotating from its first position to asecond position and separating in response to a force applied to thebreakaway support post in one direction corresponding with an impact bya vehicle with one end of the associated guardrail;

FIG. 14A is a schematic drawing in elevation with portions broken awayshowing a detail side view of a breakaway support post incorporating afurther embodiment of the present invention;

FIG. 14B is a schematic drawing in elevation with portions broken awayshowing another side view of the breakaway post of FIG. 14A;

FIG. 15A is a schematic drawing in elevation with portions broken awayshowing a detail side view of a breakaway post in accordance with stillanother embodiment of the present invention;

FIG. 15B is a schematic drawing in elevation with portions broken awayshowing the upper portion and the lower portion of the breakaway supportpost of FIG. 15A disconnected from each other;

FIG. 15C is a schematic drawing in elevation with portions broken awayshowing another side view of the breakaway support post of FIG. 15B; and

FIG. 16 is a schematic drawing in elevation with portions broken awayshowing a side view of the breakaway support post of FIG. 15A rotatingfrom its first position to a second position in response to a forcesupplied to the breakaway support post in one direction correspondingwith an impact by a vehicle with one end of an associated guardrail.

DETAILED DESCRIPTION OF THE INVENTION

The preferred embodiments of the present invention and its advantagesare best understood by referring to the FIGS. 1 through 16 of thedrawings, like numerals being used for like and corresponding parts ofthe various drawings.

Portions of highway guardrail system 20 incorporating one embodiment ofthe present invention are shown in FIGS. 1, 2 and 3. Portions of highwayguardrail systems 120, 220, and 320 incorporating alternativeembodiments of the present invention are shown in FIGS. 4 through 13.Breakaway support posts incorporating further embodiments of the presentinvention are shown in FIGS. 14A through 16. Highway guardrail systems20, 120, 220, and 320 are typically installed along the edge of ahighway or roadway (not expressly shown) adjacent to a hazard (notexpressly shown) to prevent a vehicle (not shown) from leaving theassociated highway or roadway.

Guardrail systems 20, 120, 220, and 320 are primarily designed andinstalled along a highway to withstand a rail face impact from a vehicledownstream from an associated end treatment. Various types of guardrailend treatments (not expressly shown) are preferably provided at the endof guardrail 22 facing oncoming traffic. Examples of guardrail endtreatments satisfactory for use with the present invention are shown inU.S. Pat. No. 4,655,434 entitled Energy Absorbing Guardrail Terminal;U.S. Pat. No. 4,928,928 entitled Guardrail Extruder Terminal; and U.S.Pat. No. 5,078,366 entitled Guardrail Extruder Terminal. Such guardrailend treatments extend substantially parallel with the associatedroadway. U.S. Pat. No. 4,678,166 entitled Eccentric Loader GuardrailTerminal shows a guardrail end treatment which flares away from theassociated roadway. U.S. Pat. Nos. 4,655,434; 4,928,928; 5,078,366; and4,678,166 are incorporated herein by reference. When this type ofguardrail end treatment is hit by a vehicle, the guardrail will normallyrelease from the associated support post and allow the impacting vehicleto pass behind downstream portions of the associated guardrail. However,breakaway support posts incorporating teachings of the present inventionmay be used with any guardrail end treatment or guardrail system havingsatisfactory energy-absorbing characteristics for the associated roadwayand anticipated vehicle traffic.

Support posts 30, 130, 230, 330 and 530 have a strong direction and aweak direction. When a post is subjected to an impact from the strongdirection, the post exhibits high mechanical strength. The strongdirection is typically oriented perpendicular to the guardrail. Thus,when the post is impacted by a vehicle in the strong direction (such aswhen the vehicle impacts the face of the guardrail), the post willremain intact and standing, and the vehicle will be redirected back ontothe road. When the post is subjected to an impact from the weakdirection, the post exhibits low mechanical strength. The weak directionis typically oriented parallel to the guardrail. Thus, when the post isimpacted by a vehicle in the weak direction (such as when the vehicleimpacts the end of the guardrail), the portion of the post that issubstantially above the ground will either break off or bend over, so asto avoid presenting a substantial barrier to the vehicle. Preferably,the upper portion of the post will deflect slightly and then break off,in order to minimize lifting of the impacting vehicle into the air.

One or more support posts 30, 130, 230, 330, and 530 are preferablyincorporated into the respective guardrail end treatment tosubstantially minimize damage to a vehicle during a head-on impact withthe end of guardrail 22 facing oncoming traffic. The number of supportposts 30, 130, 230, 330 and 530 and the length of guardrail 22 may bevaried depending upon the associated roadway, the hazard adjacent to theroadway requiring installation of highway guardrail system 20, 120, 220or 320, anticipated vehicle traffic on the associated roadway, and theselected guardrail end treatment. As discussed later in more detail,breakaway support posts 30, 130, 230, 330 and 530 will securely anchorguardrail 22 during a rail face impact or side impact with guardrail 22to redirect an impacting vehicle back onto the associated roadway.Support posts 30, 130, 230, 330 and 530 will yield or buckle during ahead-on impact with the end of guardrail 22 without causing excessivedamage to an impacting vehicle.

Support posts 30, 130, 230, 330 and 530 may be fabricated from varioustypes of steel alloys or other materials with the desired strengthand/or breakaway characteristics appropriate for the respective highwayguardrail system 20, 120, 220, and 320. For some applications, abreakaway support post incorporating teachings of the present inventionmay be fabricated from ceramic materials or a mixture of ceramic andmetal alloys which are sometimes referred to as cermets.

Portions of breakaway support posts 30, 130, 230, 330 and 530, as shownin FIGS. 1-16, have the general configuration associated with a steelI-beam. Alternatively, the teachings of the present invention may beincorporated into a breakaway support post having a generally hollow orsolid, rectangular, square or circular cross section.

Breakaway support posts 30, 130, 230, 330 and 530 as shown in FIGS.1-16, have respective upper portions and lower portions withapproximately the same general cross-section. However, for someapplications, the upper portion of a breakaway support postincorporating teachings of the present invention may have across-section which is substantially different from the cross-section ofthe associated lower portion. For example, the upper portion may havethe general configuration associated with an I-beam, while theassociated lower portion may have a general configuration associatedwith either a hollow or solid cylindrical post or a hollow or solidsquare post.

In FIGS. 1, 2, 4, 7 and 10, highway guardrail systems 20, 120, 220 and320 are shown having a typical deep W-beam twelve (12) gauge typeguardrail 22. For some applications, a thrie beam guardrail may besatisfactorily used. Other types of guardrails, both folded andnon-folded, may be satisfactorily used with breakaway support posts 30,130, 230, 330 and 530 incorporating the teachings of the presentinvention. Breakaway support posts 30, 130, 230, 330 and 530 maysometimes be described as direct drive support posts.

Various techniques which are well known in the art may be satisfactorilyused to install breakaway support posts 30, 130, 230, 330 and 530depending upon the type of soil conditions and other factors associatedwith the roadway and the hazard requiring installation of respectivehighway guardrail systems 20, 120, 220, and 320. For many applications,breakaway support posts 30, 130, 230, 330 and 530 may be simply driveninto the soil using an appropriately sized hydraulic and/or pneumaticdriver. As a result, breakaway support posts 30, 130, 230, 330 and 530may be easily removed from the soil using an appropriately sized craneor other type of pulling tool. For many applications, breakaway posts30, 130, 230, 330 and 530 may be satisfactorily used to installguardrail 22 adjacent to an associated roadway without the use of metalfoundation tubes or other types of post-to-ground installation systemssuch as concrete with a steel slip base support. U.S. Pat. No.5,503,495, entitled Thrie-Beam Terminal With Breakaway Post CableRelease, shows one example of a breakaway support post with this type offoundation.

As shown in FIGS. 1, 2 and 3, breakaway support post 30 includeselongated body 32 defined in part by web 34 with flanges 36 and 38attached thereto. Elongated body 32 may be formed by cutting a steelI-beam (not expressly shown) into sections having the desired length forelongated body 32. A pair of elongated slots 40 and 42 are preferablyformed in flange 36 on opposite sides of web 34. Similarly, a pair ofslots 44 and 46 are preferably formed in flange 38 on opposite sides ofweb 34. Slots 40, 42, 44 and 46 are formed intermediate first end 31 andsecond end 33 of breakaway support post 30. Slots 40, 42, 44 and 46define in part a frangible or yieldable connection between an upperportion and a lower portion of support post 30.

The length of breakaway support post 30 and the location of slots 40,42, 44 and 46 will depend upon various factors including soil conditionsand the anticipated amount of force that will be applied to breakawaysupport post 30 during a rail face impact with guardrail 22 and during ahead-on impact with one end of guardrail 22. For the embodiment shown inFIGS. 1, 2 and 3, slots 40, 42, 44 and 46 are formed in breakaway post30 at a location corresponding approximately with the anticipated groundline when breakaway support post 30 is properly installed adjacent tothe associated roadway.

For one application, elongated body 32 may be formed from a standardsteel I-beam with flanges 36 and 38 having a nominal width of four (4″)inches and web 34 having a nominal width of six (6″) inches. Slots 40,42, 44 and 46 have a generally elongated oval configurationapproximately six (6″) inches in length and one fourth (¼″) inch inwidth. Slots 40, 42, 44, and 46 are positioned intermediate ends 31 and33 to cause local buckling of the associated breakaway post 30 whenproperly installed.

For the embodiments shown in FIGS. 1 and 2, block 48 is disposed betweenbreakaway support post 30 and guardrail 22. Block 48 may sometimes bereferred to as a “blockout.” For other applications, guardrail 22 may bedirectly mounted adjacent to end 31 of breakaway support post 30. Duringa rail face impact between a vehicle and guardrail 22 downstream fromthe associated end treatment, block 48 provides a lateral offset betweenbreakaway support post 30 and guardrail 22. The distance and directionof the lateral offset is selected to prevent the wheels (not shown) ofan impacting vehicle from striking breakaway support post 30 during therail face impact.

For the embodiment shown in FIGS. 1, 2 and 3, breakaway support post 30includes soil plates 52 and 54 which are attached to the exterior ofrespective flanges 36 and 38 adjacent to the portion of breakawaysupport post 30 which will be inserted into the soil adjacent to theassociated roadway. For this embodiment, soil plates 52 and 54 haveapproximately the same thickness as web 34 and are generally alignedwith web 34 on opposite sides of respective flanges 36 and 38.

Breakaway support post 30 is preferably installed with web 34 extendedapproximately perpendicular from guardrail 22 and flanges 36 and 38extending generally parallel with guardrail 22. By aligning web 34approximately perpendicular to guardrail 22, breakaway support post 30will provide sufficient support to resist large forces associated with arail face impact or rail face impact between a vehicle and guardrail 22.As a result of forming slots 40, 42, 44 and 46 in respective flanges 36and 38 and orienting flanges 36 and 38 generally parallel with guardrail22, a head-on impact from a vehicle with one end of guardrail 22 willresult in buckling or yielding of breakaway support post 30.

The amount of force required to buckle and/or fracture breakaway supportpost 30 may be decreased by increasing the size and/or the number ofslots 40, 42, 44 and 46 formed in respective flanges 36 and 38.Alternatively, reducing the number and/or size of slots 40, 42, 44 and46 will result in a larger amount of force required to buckle or yieldbreakaway support post 30.

The orientation of soil plates 52 and 54, relative to a head-on impactwith one end of guardrail 22 will prevent twisting or tilting ofbreakaway support post 30 during the head-on impact. The additionalsupport provided by soil plates 52 and 54 will increase the reliabilityof breakaway support post 30 yielding or buckling at the generallocation of slots 40, 42, 44 and 46 in response to a selected amount offorce applied adjacent to end 31 of post 30 in a first directioncorresponding to the direction of a head-on impact with one end ofguardrail 22. Soil plate 52 includes a generally triangular portion 56which extends above elongated slots 40, 42, 44 and 46 to provideadditional support for breakaway support post 30 and guardrail 22 duringa rail face impact.

For some applications, the length of elongated body 32 may be increasedsuch that soil plates 52 and 54 are no longer required to provideadditional support for the resulting breakaway support post 30.Eliminating soil plates 52 and 54 will allow a hydraulic or pneumatichammer to more quickly install the associated breakaway support post 30and a crane or hydraulic/pneumatic pulling tool to more easily remove adamaged breakaway support post 30. Alternatively, breakaway support post30 could be inserted into an appropriately sized concrete foundationand/or metal sleeve. Soil plates, concrete foundation, sleeves and otheranchoring devices can be used in any of the posts of the presentinvention.

For some applications, it may be preferable to form a breakaway supportpost in accordance with teachings of the present invention from anelongated body having a generally hollow, rectangular or squareconfiguration (not shown). Slots 40, 42, 44 and 46 may then be formed inopposite sides of the resulting breakaway support post which are alignedgenerally parallel with the associated guardrail similar to flanges 36and 38. The other pair of opposite sides preferably extend approximatelynormal from the associated guardrail similar to web 34.

When force is applied adjacent to end 31 of breakaway support post 30 ina second direction corresponding with a rail face impact between avehicle and guardrail 22, web 34 will resist buckling of breakawaysupport post 30 and provide sufficient support to redirect the impactingvehicle back onto the roadway.

Breakaway support post 130, as shown in FIGS. 4, 5 and 6, includeselongated body 132 having an upper portion 142 and a lower portion 144which are rotatably coupled with each other. For the embodiment of thepresent invention shown in FIGS. 4, 5 and 6, rotatable coupling assembly140 is preferably installed intermediate ends 131 and 133 of elongatedbody 132.

Upper portion 142 and lower portion 144 each have a generalconfiguration of an I-beam defined in part by respective webs 134 andflanges 136 and 138. Upper portion 142 and lower portion 144 may beformed from a conventional steel I-beam in the same manner as previouslydescribed.

For the embodiment of the present invention as shown in FIGS. 4, 5 and6, rotatable coupling assembly 140 includes a first generally U-shapedbracket 150 attached to one end of upper portion 142, opposite end 131and a second U-shaped bracket 152 attached to the end of lower portion144 opposite from end 133. Brackets 150 and 152 each have a generallyopen, U-shaped configuration with extensions substantially parallel tothe flanges and protruding beyond the respective webs. A portion ofbracket 150 is preferably sized to fit within a corresponding portion ofbracket 152. Pivot pin 154 extends laterally through adjacent portionsof bracket 150 and 152 in a direction which is generally parallel withwebs 134. The resulting breakaway support post 130 is preferablyinstalled with webs 134 and pivot pin 154 extending generally normalfrom the associated guardrail 22. As a result of this orientation, webs134 and rotatable coupling assembly 140 including pivot pin 154 allowbreakaway support post 130 to sufficiently support guardrail 22 during arail face impact to redirect an impacting vehicle back onto theassociated roadway.

In FIGS. 4, 5 and 6, respective webs 134 of upper portion 142 and lowerportion 144 are shown generally aligned parallel with each other. Forsome applications, the orientation of lower portion 144 may be variedwith respect to upper portion 142 such that web 134 of lower portion 144extends approximately parallel with guardrail 22. The attachment ofbrackets 150 and 152 with their respective upper portion 142 and lowerportion 144 may be modified to accommodate various orientations of lowerportion 144 relative to upper portion 142.

Depending upon the length of lower portion 144 and the type of soilconditions, soil plates 162 and 164 may be attached to lower portion 144extending from respective flanges 136 and 138. For some applications,lower portion 144 may be substantially longer than upper portion 142. Asa result of increasing the length of lower portion 144, the use of soilplates 162 and 164 may not be required.

Shear pin 156 is laterally inserted through adjacent portions ofbrackets 150 and 152 offset from pivot pin 154. Shear pin 156 preferablyhas a relatively small cross-section as compared to pivot pin 154. As aresult, when a vehicle impacts with one end of guardrail 22, shear pin156 will break and allow upper portion 142 to rotate relative to lowerportion 144 as shown in FIG. 6. Shear pin 156 maintains upper portion142 and lower portion 144 generally aligned with each other duringinstallation of the associated breakaway support post 30.

The amount of force required to fracture or break shear pin 156 may bedetermined by a variety of parameters such as the diameter of shear pin156, the type of material used to fabricate shear pin 156, the number oflocations (either along a single pin or with plural pins) that must besheared, and the distance between shear pin 156 and pivot pin 154. Asdiscussed later in more detail with respect to breakaway support post530, as shown in FIGS. 15A through 16, rotatable coupling 540 may bemodified to allow upper portion 542 to disconnect and separate fromlower portion 544.

Various types of releasing mechanisms other than shear pin 156 may besatisfactorily used to maintain upper portion 142 and lower portion 144generally aligned with each other during normal installation and use ofthe associated breakaway support post 130. A wide variety of shearbolts, shear screws and/or breakaway clamps may be used to releasablyattach first bracket 150 with second bracket 152.

When a vehicle impacts with one end of guardrail 22, force is applied ina first direction to upper portion 142 and will break shear pin 156. Asa result, upper portion 142 will then rotate relative to lower portion144 as shown in FIG. 6.

FIGS. 7, 8 and 9 show portions of highway guardrail system 220 whichincludes breakaway support post 230 and guardrail 22. Breakaway supportpost 230 includes elongated body 32 and is similar in both design andfunction with breakaway support post 30. One difference betweenbreakaway support posts 30 and 230 is the replacement of soil plates 52and 54 by soil plates 254 and 256. As best shown in FIGS. 8 and 9,fastener assembly 160 may be used to attach soil plate 254 withelongated body 32. Fastener assembly 160 includes threaded bolt 163,hollow sleeve or spacer 168 and nut 165. The use of soil plate 254 andfastener assembly 160 eliminates some of the welding steps associatedwith attaching soil plates 52 and 54 to breakaway support post 30.

Soil plate 254 has a generally rectangular configuration. The length,width and thickness of soil plates 254 may be varied depending upon theintended application for the associated breakaway post 230 and theanticipated soil conditions adjacent to the associated roadway. Anappropriately sized hole is preferably formed in the mid-point of soilplate 254 and bolt 163 inserted therethrough. The head 166 of bolt 162is disposed on the exterior of soil plate 254. Spacer or hollow sleeve168 is then fitted over the threaded portion of bolt 163 extending fromsoil plate 254 opposite from head 166. A corresponding hole ispreferably formed in web 34 at the desired location for soil plate 254.Bolt 163 is inserted through the hole in web 34 and nut 165 attachedthereto.

For some applications, a smaller soil plate 256 may be attached to theexterior of flange 36 adjacent to web 34. The dimensions and location ofsoil plate 256 may be varied depending upon the anticipated applicationincluding soil conditions, associated with highway guardrail system 220.

FIGS. 10 and 11 illustrate portions of highway guardrail system 320,which includes breakaway support post 330 and guardrail 22. FIG. 11illustrates an embodiment of support post 330 having narrower breakerbars 350 and 352 than those illustrated in FIG. 10. Support post 330includes an elongated body 332 having an upper portion 342 and a lowerportion 344. Upper portion 342 and lower portion 344 each have thegeneral configuration of a steel I-beam similar to elongated body 32 ofbreakaway support post 30.

Upper portion 342 and lower portion 344 are defined in part byrespective webs 334 and flanges 336 and 338. Upper portion 342 and lowerportion 344 may be formed from a conventional steel I-beam in the samemanner as previously described. Lower portion 344 may be positionedsubstantially within the ground. Alternatively, lower portion 344 couldbe inserted into a concrete foundation and/or a metal sleeve which havebeen previously installed at the desired roadside location.

Upper portion 342 and lower portion 344 are provided with breaker bars350 and 352. In the embodiment shown in FIG. 10, flanges 336 and 338 inupper portion 342 are connected to breaker bar 350, by for example,welds. Flanges 336 and 338 in lower portion 344 may be connected tobreaker bar 352 in an analogous fashion. Other suitable connectiontechniques may be used to couple flanges 336 and 338 of upper and lowerportions 342 and 344 to breaker bars 350 and 352, respectively. Forexample, as illustrated in FIG. 11, tie straps 362 and 364 may be used,particularly in an embodiment where breaker bars 350 and 352 arenarrower than flanges 336 and 338, as is the case in FIG. 11. For someapplications, breaker bar 352 may be directly attached to a concretefoundation to eliminate the use of lower portion 344.

Breaker bars 350 and 352 are connected to each other by fasteners 358,which is illustrated by a simple nut and bolt; however, other suitablefasteners may be used with this aspect of the invention. Breaker bars350 and 352 are preferably formed with chamfered or tapered surfaces354. Chamfered surfaces 354 cooperate with each other to define in parta notch or gap between adjacent portions of breaker bars 350 and 352.Chamfered surfaces 354 extend generally parallel with each other in adirection generally normal to guardrail 22. An imaginary line 359 canalso be drawn through fasteners 358 in the same general directionparallel with chamfered surfaces 354 and normal to guardrail 22.Imaginary line 359 corresponds with a strong direction for breakawaysupport posts 330 in which breakaway support post 330 exhibits highmechanical strength. There is a notch or gap on each side of theimaginary line 359.

Chamfered surfaces 354 cooperate with each other to allow upper portion342 to pivot relative to lower portion 344 during a head-on impact, asillustrated in FIG. 11. Such pivoting may cause fasteners 358 to break,separating upper portion 342 from lower portion 344 and may thereforesubstantially minimize damage to a vehicle during a head-on impact withthe end of guardrail 22 facing oncoming traffic. The orientation ofchamfered surfaces 354 and fasteners 358 relative to each other furtherdefine a weak direction for breakaway support post 330 in which supportpost 330 exhibits low mechanical strength. However, chamfered surfaces354 do not reduce the ability of guardrail 320 to redirect an impactingvehicle back onto the associated roadway during a rail face impact withguardrail 22.

FIG. 12 is a schematic drawing showing an exploded isometric view withportions broken away of an alternative embodiment of breaker barssuitable for use in guardrail system 320. Breaker bars 450 and 452perform similar functions as breaker bars 350 and 352. Breaker bar 450includes a flat plate 453 having a protruding member or projection 454.Breaker bar 452 includes a flat plate 455 having a protruding member orprojection 456. Flat plates 453 and 455 are each formed with two or moreapertures 458 for receiving a connecting member, such as mechanicalfastener 358, for attaching breaker bars 450 and 452 with each other.The use of protruding members or projections 454 and 456 allows upperportion 342 to pivot relative to lower portion 344 during a head-onimpact, as illustrated in FIG. 13. Impact from the weak direction forsupport post 330 will result in bending and preferably failure ofconnecting members 358. Failure of connecting members 358 separatesupper portion 342 from lower portion 344 and may, therefore,substantially minimize damage to a vehicle during a head-on impact withthe end of guardrail 22 facing oncoming traffic. However, protrudingmembers or projections 454 and 456 do not reduce the ability ofguardrail 22 to redirect an impacting vehicle back onto the associatedroadway during a rail face impact.

FIGS. 14A and 14B are schematic drawings with portions broken awayshowing an alternative embodiment of a frangible or yieldable connectionsatisfactory for releasably coupling upper portion 342 with lowerportion 344 of support post 330. For this embodiment, breaker bars 450and 452 are substantially the same as previously described with respectto the embodiment shown in FIG. 13, except for the elimination ofprotruding members or projections 454 and 456. A pair of elongatedconnecting members 458 and a plurality of nuts 460 are preferablyprovided to maintain a desired gap or spacing between breaker bars 450and 452. For the embodiment shown in FIGS. 14A and 14B, elongatedconnecting members 458 and nuts 460 have matching threads. However,various types of mechanical fasteners and connecting members may besatisfactorily used to position upper portion 332 of support post 330relative to lower portion 344.

As a result of incorporated teachings of the present invention, supportpost 330 has relatively low mechanical strength with respect to impactfrom a direction generally normal to an imaginary line 359 (see FIG. 10)extending through connecting members 358 or 458 as appropriate. Thisdirection may be referred to as the “weak direction.” Connecting members358 and 458 are preferably formed from materials which will yield andpreferably fracture or break to allow upper portion 342 to separate fromlower portion 344. Since there is a gap between the breaker bars 350 and352 or breaker bars 450 and 452 to either side of line 359 in the weakdirection, connecting members 358 or 458 as appropriate will carrysubstantially all of the force or load from an impact in the weakdirection.

When support post 330 is impacted from another direction, the resultingforce, or at least a component of the resulting force, will tend toplace one of the associated connecting members 358 or 458 as appropriatein tension, and will tend to place the other connecting member 358 or458 as appropriate in compression. Therefore, the mechanical strength ofthe frangible connection between upper portion 342 and lower portion 344is substantially greater in the strong direction as compared with animpact from the weak direction. The strongest direction for an impactwith support post 330 is from a direction substantially perpendicular tothe surface of flanges 338 and 336 and parallel with web 334 (the strongdirection). The weakest direction for an impact with support post 330 isin a direction which is substantially perpendicular to web 334 andparallel with flanges 336 and 338.

Spacers with various forms and configurations may be used to separatebreaker bars 350 and 352 or 450 and 452 from each other as desired. Forthe embodiment shown in FIGS. 10 and 11, tapered surfaces or chamferedsurfaces 354 form the necessary spacers as integral components ofbreaker bars 350 and 352. For the embodiment shown in FIGS. 12 and 13,protruding members or projections 454 and 456 function as spacers toform the desired gap. For the embodiment shown in FIGS. 14A and 14B,nuts 460 cooperate with connecting members 458 to function as spacers toform the desired gap. Nuts 460 that are between breaker bars 450 and 452may also be referred to as “stops.”

For some applications, upper portion 342 and lower portion 344 ofsupport post 330 may be coupled with each other by only one connectingmember 358 or 458. Alternatively, more than two connecting members 358or 458 may be used depending upon the anticipated application for theassociated support post 330. For some applications, one connectingmember 358 or 458 may be provided on the side of support post 330 whichis immediately adjacent to guardrail 22. The associated breaker bars 350and 352 or 450 and 452 will contact each other on the opposite side ofthe post, whereby the single connecting member 358 or 458 as appropriatewill provide sufficient strength for support post 330 to withstand railface or side impact with the associated guard rail 22.

Support post 530, as shown in FIGS. 15A through 16, is substantiallysimilar to previously described support post 130, except rotatablecoupling assembly 140 has been replaced by rotatable coupling assemblyor releasable hinge 540. The embodiment shown in FIGS. 15A, 15B, 15C and16 provides for the separation of upper portion 142 from lower portion144. Thus, upper portion 142 will not lift an impacting vehicle. Supportpost 530 may be formed in part by upper portion 142 and lower portion144 as previously described with respect to support post 130. Couplingassembly or releasable hinge 540 preferably includes a first generallyU-shaped bracket 550 attached to one end of upper portion 142, and asecond U-shaped bracket 552 attached to an adjacent end of lower portion144. Brackets 550 and 552 each have a generally open, U-shapedconfiguration. A portion of bracket 550 is preferably sized to fit overa corresponding portion of bracket 552.

Pivot pin 554 preferably extends through adjacent portions of brackets552 in a direction which is generally parallel with webs 134.Alternatively, pivot pin 554 may be replaced by generally roundprojections extending from opposite sides of bracket 552. Bracket 550preferably includes a pair of slots 572 formed in opposite sidesthereof. Slots 572 are preferably sized to releasably engage respectiveportions of pin 554 which extend from bracket 552. Slots 572 cooperatewith pivot pin 554 to allow rotation of upper portion 142 relative tolower portion 144, and to allow disengagement of upper portion 142 fromlower portion 144.

The resulting breakaway support post 530 is preferably installed withwebs 134 and pivot pin 554 extending generally normal from theassociated guardrail 22. As a result of this orientation, webs 134 andreleasable hinge 540, including pivot pin 554, allow support post 530 toadequately support guardrail 22 during a rail face impact to redirect animpacting vehicle back onto the associated roadway.

Shear pin 556 is preferably inserted through adjacent portions ofbrackets 550 and 552 offset from pivot pin 554. Shear pin 556 maintainsupper portion 142 and lower portion 144 generally aligned with eachother during installation of the associated breakaway support post 530.Shear pin 556 preferably has a relatively small cross-section ascompared to pivot pin 554. As a result, when a vehicle impacts with oneend of guardrail 22, shear pin 556 will break and allow upper portion142 to rotate relative to lower portion 144 as shown in FIG. 16. Forsome applications, push bar 580 is preferably attached to and extendsbetween opposite sides of bracket 552. The location of push bar 580 onbracket 552 is selected to assist disengagement of slot 572 from pivotpin 554 as upper portion 142 rotates relative to lower portion 144. SeeFIG. 16.

The amount of force required to fracture or break shear pin 556 may bedetermined by a variety of parameters such as the diameter of shear pin556, the type of material used to fabricate shear pin 556, the number oflocations (either along a single pin or with plural pins) that must besheared, and the distance between shear pin 556 and pivot pin 554.

Various types of releasing mechanisms other than shear pin 556 may besatisfactorily used to maintain upper portion 142 and lower portion 144generally aligned with each other during normal installation and use ofthe associated breakaway support 530. A wide variety of shear bolts,shear screws, frangible disks, and/or breakaway clamps may be used toreleasably attach first bracket 550 with second bracket 552.

When a vehicle impacts with one end of guardrail 22, force is applied ina first direction (weak direction) to upper portion 142 and will breakshear pin 556. As a result, upper portion 142 will then rotate relativeto lower portion 144 as shown in FIG. 16. When portions of bracket 550contact push bar 580, slots 572 will disengage from pivot pin 554 andrelease upper portion 142 from lower portion 144.

Although the present invention and its advantages have been described indetail it should be understood that various changes, substitutions, andalterations can be made hereto without departing from the spirit andscope of the invention as defined by the following claims.

1. A breakaway guardrail post for highway crash control systemscomprising: an upper post member having a weak impact axis and a strongimpact axis; a lower post member disposed beneath and spaced apart fromsaid upper post member; a connecting joint member having a first end anda second end, said first end of said joint member connected at saidfirst end by a first fastener to said upper post member and connected atsaid second end by an attachment to said lower post member, said firstfastener having a first failure strength less than a second failurestrength of said attachment; said first fastener having a firstconnector having a first failure strength and a second connector havinga second failure strength; and said first failure strength of said firstconnector greater than said second failure strength of said secondconnector such that upon an impact force being applied along said weakimpact axis, said second connector fails and said upper post memberrotates about said first connector.
 2. A breakaway guardrail post forhighway crash control systems comprising: an upper post member having aweak impact axis and a strong impact axis; a lower post member disposedbeneath and spaced apart from said upper post member; a connecting jointmember having a first end and a second end, said first end of said jointmember connected at said first end by a first fastener to said upperpost member and connected at said second end by a second fastener tosaid lower post member, said first fastener having a first failurestrength less than a second failure strength of said second fastener;said first fastener having a first connector having a first failurestrength and a second connector having a second failure strength; andsaid first failure strength of said first connector greater than saidsecond failure strength of said second connector such that upon animpact force being applied along said weak impact axis, said secondconnector fails and said upper post member rotates about said firstconnector.